SCALEKEY BENEFITS ANAEROBIC DIGESTION

METHANE AND WASTE DIVERSION SYSTEMReducing greenhouse gas emissions and organic food waste from multi-residential buildings.

MOTIVATION

URBAN IMPACTENGINEERING DESIGN DIGESTER

Design Team: Sheldon Fernandes, Sebastian Hernandez, Sadie Hewgill, Jennifer IkertSupervisor: Professor P. Fieguth, Department Chair, Systems Design EngineeringSpecial Thanks: Elsayed El-Ebishbeshy, Mark Sobon, Ryan Walker, Orion Bruckman

Organic food waste from multi-residential buildings often ends up in landfills, where it produces methane (CH4), a greenhouse gas with 21 times the greenhouse potency of carbon dioxide (CO2); existing waste management practices and systems such as Green Bin Programs do not address this issue in an effective manner.

• New multi-residential buildings

COLLECTION SYSTEM SPECIFICATIONS

DIGESTER SPECIFICATIONS

ECONOMIC FEASIBILITY

EXPERIMENT AND DATA ANALYSIS

• Test the effect of regular and anti-bacterial soaps on different food waste compositions• Investigate the reasons for minimal effect of higher soap concentrations on methane production• Repeat the experiment to verify results

FUTURE WORK

• In the absence of oxygen, organic matter is broken down by micro-organisms• In an enclosed vessel, the process produces biogas and digestate• Biogas consists primarily of methane and carbon dioxide

Goal: test the effect of regular soap and anti-bacterial soap on methane production in an anaerobic digester using organic food waste as an input

• Multi-residential building organic waste diversion rates are very low• Our system can fill the void of existing waste management systems

City Multi-residential Organic Waste Diversion Rate

Relevant Comparator Diversion Rate

Toronto 24% 66% (single-family homes)Vancouver 16% 46% (single-family homes)Hamilton 11% 49% (overall city)

Formulation:Cost [$/year•person] = Waste [kg/year•person] * ((-Price of gas [$/m3] * Gas production rate [m3/kg]) + Capital cost [$/kg] + Operating cost [$/kg]) + Cost of collection system [$/year•person]

Waste production rate 86.000 Kg/person•yearBiogas production/kg (from fruit and vegetables) 0.032 m3/kgDigester capital cost (amortized over 8 years) 0.069 $/kgOperating cost 0.088 $/kgWaste collection system (amortized over 8 years) 26.000 $/yearNet revenue/person•year -39.100 $/person/yearCost estimation, amortized over 8 years: $39.10 per person per year

Simplifications: • Cost of the digester is represented by a linear function• Estimate derived from much larger system - actual cost is likely larger due to economy of scale

• Captures methane from decomposing organic food waste• Harnesses energy produced from burning methane• Does not place additional load on wastewater treatment plants• User collection system for organic waste collection and disposal is convenient and easy• No indoor storage of decaying organics required

• Garbage disposal located under each sink grinds food waste when switch is activated• Switch also triggers automated valve to divert sink output to digester• When switch is not activated, valve directs sink discharge to municipal wastewater processing• Waste is routed to digester using water as transport mechanism• Additional piping network throughout building collects organic waste from individual sinks• Gas trap located on the wastewater pipeline to prevent gases from municipal plants entering units• Gas trap not required on the digester pipeline, as the valve blocks gases from entering units• Both sets of piping are vented to common stack

• Low-solids o Water is used to transport waste• Continuous o Continuous input of organic waste• Mesophilic (35-40°C) o Bacterial populations more robust and adaptable to changing conditions o Lower energy input to maintain temperature• Single-stage o Lower capital cost o Easier to operate o Fewer technical failures

To municipal wastewater treatment

To digester

Garbage disposal

Electronic actuator

Valve to switch between digester and wastewater output

From sink

All organic waste proceeds to digester

References:[1] Arsova, L. (2010). Anaerobic digestion of food waste: Current status, problems and an alternative product. Master’s Thesis, Columbia University, Department of Earth and Environmental Engineering.[2] Best, J. (2011). Best Practices for Multi-Family Food Scraps Collection. Background Paper, Recycling Council of British Columbia.[3] Stantec Consulting Ltd. (2012). Multi-Family Diversion Program Best Practices. The City of Calgary, Multi-Family Waste DiversionStakeholder Engagement & Strategy.

Digester inputGas output

Digester output

Pump to discharge digestate

Tank

Mixer

• Prototype: construction of an in-unit waste collection system• Design: from food waste input to methane and byproduct outputSCOPE

FUTURE WORK

Methodology: duplicate batch tests were conducted at the ideal temperature for mesophilic digestion (37ºC) in an incubator at 180 rpm with three different concentrations: o Low: 0.04 mL/L o Medium: 0.4 mL/L o High: 4 mL/L

Results:• Low concentrations of both soaps produced less methane• High concentrations for both soaps produced approximately the same amount of methane• High concentrations inhibited the production of methane less than low and

FUTURE WORK• Gather feedback from potential customers such as building managers and tenants• Formulate a more accurate estimate of cost using a smaller digester

• Test the actuator for the valve• Include the handling of digestate in scope

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Cumula&

ve  CH4  P

rodu

c&on

 [mL]  

Day  

Cumula&ve  CH4  Produc&on  with  Seed  Subtracted  

Food  &  Seed  

Regular  Soap  -­‐  Low  

Regular  Soap  -­‐  Med  

Regular  Soap  -­‐  High  

An=  Soap  -­‐  Low  

An=  Soap  -­‐  Med  

An=  Soap  -­‐  High